(i) Tetraamminediaquacobalt(III) chloride : [CO(H2O) 2(NH3)4]Cl3 (ii) Potassium tetracyanonickelate(II) : K2[Ni(CN)4] (iii) Tris(ethane?1,2?diamine) chromium(III) chloride : [Cr(en) 3]Cl3 (iv) Amminebromidochloridonitrito-N-platinate(II) : [Pt(NH3)BrCl(NO2)]- (v) Dichloridobis(ethane?1,2?diamine)platinum(IV) nitrate : [PtCl2(en) 2](NO3)2 (vi) Iron(III) hexacyanoferrate(II) : Fe4[Fe(CN) 6]3
(i) Hexaamminecobalt(III) chloride (ii) Pentaamminechloridocobalt(III) chloride (iii) Potassium hexacyanoferrate(III) (iv) Potassium trioxalatoferrate(III) (v) Potassium tetrachloridopalladate(II) (vi) Diamminechlorido(methylamine)platinum(II) chloride
Werners postulates explain the bonding in coordination compounds as follows: (i) A metal exhibits two types of valencies namely, primary and secondary valencies. Primary valencies are satisfied by negative ions while secondary valencies are satisfied by both negative and neutral ions. In modern terminology, the primary valency corresponds to the oxidation number of the metal ion, whereas the secondary valency refers to the coordination number of the metal ion. (ii) A metal ion has a definite number of secondary valencies around the central atom. Also, these valencies project in a specific direction in the space assigned to the definite geometry of the coordination compound. (iii) Primary valencies are usually ionizable, while secondary valencies are non-ionizable.
(NH4)2SO4 + 6 H2O ? FeSO4.(NH4)2SO4. 6H2OMohrs salt CuSO4 + 4NH3 + 5 H2O ? [Cu(NH3)4]SO4. 5H2Otetraamminocopper(ii)sulphate Both the compounds i.e., FeSO4.(NH4)2SO4. 6H2O and [Cu(NH3)4]SO4. 5H2O fall under the category of addition compounds with only one major difference i.e., the former is an example of a double salt, while the latter is a coordination compound. A double salt is an addition compound that is stable in the solid state but that which breaks up into its constituent ions in the dissolved state. These compounds exhibit individual properties of their constituents. For e.g. FeSO4.(NH4)2SO4. 6H2O breaks into Fe2+ , NH4+ , and SO42? ions. Hence, it gives a positive test for Fe2+ ions. A coordination compound is an addition compound which retains its identity in the solid as well as in the dissolved state. However, the individual properties of the constituents are lost. This happens because [Cu(NH3)4]SO4. 5H2O does not show the test for Cu2+ . The ions present in the solution of [Cu(NH3)4]SO4. 5H2O are [Cu(NH3)42+ and SO42- .
(i) [Zn(OH]2? (ii) K2[PdCl4] (iii) [Pt(NH3)2Cl2] (iv) K2[Ni(CN) 4] (v) [Co(ONO) (NH3)5]2+ (vi) [Co(NH3)6]2 (SO4)3] (vii) K3[Cr(C2O4)3] (viii) [Pt(NH3)6]4+ (ix) [Cu(Br) 4]2? (x) [Co[NO2)(NH3)5]2+
(i) Hexaamminecobalt(III) chloride (ii) Diamminechlorido(methylamine) platinum(II) chloride (iii) Hexaquatitanium(III) ion (iv) Tetraamminichloridonitrito-N-Cobalt(III) chloride (v) Hexaquamanganese(II) ion (vi) Tetrachloridonickelate(II) ion (vii) Hexaamminenickel(II) chloride (viii) Tris(ethane-1, 2-diammine) cobalt(III) ion (ix) Tetracarbonylnickel(0)
Aqueous CuSO4 exists as [Cu(H2O) 4]SO4. It is blue in colour due to the presence of [Cu[H2O) 4]2 ions. (i) When KF is added:[Cu(H2O)4]2+ + 4F- ? [Cu(F) 4]2- (green)+ 4H2O (ii) When KCl is added:[Cu(H2O]2+ + 4 Cl- → [CuCl4]2-(bright green> + H2O In both these cases, the weak field ligand water is replaced by the F- and Cl- ions.
CuSO4 + 4KCN + 4KCN ? K2[Cu(CN) 4] + K2SO4 i.e. [Cu(H2O) 4]2+ + 4 CN- → [Cu(CN) 4]2- + 4H2O Thus, the coordination entity formed in the process is K2 [Cu(CN) 2]. is a very stable complex, which does not ionize to give Cu2+ ions when added to water. Hence, Cu2+ ions are not precipitated when H2S(g) is passed through the solution.
A spectrochemical series is the arrangement of common ligands in the increasing order of their crystal-field splitting energy (CFSE) values. The ligands present on the R.H.S of the series are strong field ligands while that on the L.H.S are weak field ligands. Also, strong field ligands cause higher splitting in the d orbitals than weak field ligands. I- < Br- < S2- < SCN- < Cl- < N3 < F- < OH- < C2O42- < H2O < NCS- < H- < CN- < NH3 < en(ethylenediamine) < SO32- < NO2- < phen < CO.
The degenerate d-orbitals (in a spherical field environment) split into two levels i.e., eg and t2g in the presence of ligands. The splitting of the degenerate levels due to the presence of ligands is called the crystal-field splitting while the energy difference between the two levels (eg and t2g) is called the crystal-field splitting energy. It is denoted by ?o . After the orbitals have split, the filling of the electrons takes place. After 1 electron (each) has been filled in the three t2g orbitals, the filling of the fourth electron takes place in two ways. It can enter the eg orbital (giving rise to t t2g 3 eg1 like electronic configuration) or the pairing of the electrons can take place in the t t2g orbitals (giving rise to t t2g 4 eg0 like electronic configuration). If the ?o value of a ligand is less than the pairing energy (P), then the electrons enter the eg orbital. On the other hand, if the ?o value of a ligand is more than the pairing energy (P), then the electrons enter the t2g orbital.
In [Ni(H2O)6]2+, H2O is a weak field ligand. Therefore, there are unpaired electrons in Ni2+. In this complex, the d electrons from the lower energy level can be excited to the higher energy level i.e., the possibility of d?d transition is present. Hence, Ni(H2O)6]2+is coloured. In [Ni(CN) 4]2?, the electrons are all paired as CN- is a strong field ligand. Therefore, d-d transition is not possible in [Ni(CN) 4]2?. Hence, it is colourless.
The colour of a particular coordination compound depends on the magnitude of the crystal-field splitting energ916;. This CFSE in turn depends on the nature of the ligand. In case of [Fe(CN)6]4? and [Fe(H2O)6]2+ , the colour differs because there is a difference in the CFSE. Now, CN? is a strong field ligand having a higher CFSE value as compared to the CFSE value of water. This means that the absorption of energy for the intra d-d transition also differs. Hence, the transmitted colour also differs.
(i) K3[Co(C2O4)3]
The central metal ion is Co.
Its coordination number is 6.
The oxidation state can be given as:
x ? 6 = ?3
x = 3
The d orbital occupation for Co3 is t2g6eg0.
(ii) cis-[Cr(en) 2Cl2]Cl
The central metal ion is Cr.
The coordination number is 6.
The oxidation state can be given as:
x + 2(0) + 2(?1) = 1
x ? 2 = 1
x = 3
The d orbital occupation for Cr3 is t2g3eg0.
(iii) (NH4)2[CoF4]
The central metal ion is Co.
The coordination number is 4.
The oxidation state can be given as:
x ? 4 = ?2
x = 2
The d orbital occupation for Co2 is eg4 t2g3.
(iv)[Mn(H2O) 6]SO4
The central metal ion is Mn.
The coordination number is 6.
The oxidation state can be given as:
x + 0 = +2
x = +2
The d orbital occupation for Mn is t2g3 eg2.
(i) Role of coordination compounds in biological systems: We know that photosynthesis is made possible by the presence of the chlorophyll pigment. This pigment is a coordination compound of magnesium. In the human biological system, several coordination compounds play important roles. For example, the oxygen-carrier of blood, i.e., haemoglobin, is a coordination compound of iron. (ii) Role of coordination compounds in medicinal chemistry: Certain coordination compounds of platinum (for example, cis-platin) are used for inhibiting the growth of tumours. (iii) Role of coordination compounds in analytical chemistry: During salt analysis, a number of basic radicals are detected with the help of the colour changes they exhibit with different reagents. These colour changes are a result of the coordination compounds or complexes that the basic radicals form with different ligands. (iii) Role of coordination compounds in extraction or metallurgy of metals: The process of extraction of some of the metals from their ores involves the formation of complexes. For example, in aqueous solution, gold combines with cyanide ions to form [Au(CN)2]. From this solution, gold is later extracted by the addition of zinc metal.
(iii) The given complex can be written as Co(NH3)6Cl2 Thus[Co(NH3)6]+ along with two Cl? ions are produced.